This invention relates to a needle roller bearing mounted in a universal joint.
There is known an automotive steering device for steering vehicle wheels by the rotation of a steering wheel. It comprises steering shafts for transmitting the rotation of the steering wheel to a steering box, the steering shafts including two shafts having an angle relative to each other and coupled together by a universal joint for transmission of a turning torque.
FIGS. 3A, 3B show a universal joint used in such a steering device. The universal joint has a pair of yokes 20 each having a bifurcated piece 21 formed with a bearing hole 22 into which is inserted a trunnion 24 formed on a spider 23. Each trunnion 24 is rotatably supported by a shell type needle roller bearing 30 pressed into the bearing hole 22.
The shell type needle roller bearings 30 each comprise an outer ring 31 comprising a cylindrical portion 31a pressed into the bearing hole 22 and having a bottom 31b at one end, and a plurality of needle rollers 33 rollable along a raceway 32 on the inner circumferential surface of the cylindrical portion 31a. The outer ring 31 is formed by pressing a thin metal sheet.
In the universal joint, if there is a radial gap xcex94r between the trunnions 24 of the spider 23 and the needle roller bearings 30, shaky motion resulting from the radial gap will occur between the joint portions of the pair of yokes 20, making it impossible to smoothly transmit torque between the two shafts each connected to the yokes 20.
Thus, for a steering device, in order to improve the turning operability of the steering wheel, it is desired to narrow radial gaps between the needle roller bearings and the trunnions. For this purpose, trials have been made to narrow the tolerance of dimensions of the parts. With the exception of the spiders 23, the yokes 20 and the outer rings 31 of the needle roller bearings 30 are formed by pressing. Thus there were limitations.
Heretofore, after the shell type needle roller bearing 30 has been pressed into the bearing hole 22 of each yoke 20, a trunnion 24 having an outer diameter suitable for the needle roller bearing 30 is selected and combined.
For such a universal joint of a type in which after the needle roller bearing 30 has been pressed in, a trunnion 24 is selected and combined, assembling is extremely troublesome and time-consuming.
An object of this invention is to provide a shell type needle roller bearing for a universal joint which can eliminate radial gaps.
According to this invention, there is provided a shell type needle roller bearing for a universal joint having a yoke, the needle roller comprising an outer ring made of a thin metal sheet and including a cylindrical portion having a bottom at one end thereof and an inner raceway and adapted to be inserted into a bearing hole formed in a bifurcated piece of the yoke, and a plurality of needle rollers arranged so as to be rollable along the inner raceway of the cylindrical portion, characterized in that the cylindrical portion is formed by a plurality of arcuate wall portions having their circumferential lengths substantially equal to each other.
With this arrangement, when the trunnion of the spider is inserted into the needle roller bearing, the intermediate portion of each of the arcuate wall portions forming the cylindrical portion is deformed radially outwardly by the trunnion through the needle rollers. The rollers are therefore biased against the cylindrical surface of the trunnion by the arcuate wall portions. This eliminate any radial gaps present between the needle roller bearing and the trunnion.
The arcuate walls may extend the entire width of the outer ring or only part thereof. But to stably support the needle rollers, their width has to be equal to or greater than ⅓ of the axial width of the outer ring.
To stably mount the outer ring in the bearing hole, the number of arcuate wall portions is preferably 3 or more.
There exist radial gaps of 5-6 xcexcm or greater in a conventional shell type roller bearing in a universal joint, and such large radial gaps cause various problems. Thus, if the roundness of the outer circumferential surface of the cylindrical portion formed by the arcuate wall portions is 3 xcexcm or greater it is possible to completely eliminate the radial gaps.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: